1. Field of the Invention
The present invention relates to an ATM (Asynchronous Transfer Mode) switching system in an ATM network, and more particularly to a method and system for monitoring a cell buffer use rate in the ATM switching system.
2. Description of the Art
In general, an ATM switching system is provided with a cell buffer for each input/output port. Traffic such as voice/data in ATM cells is transferred from an input cell buffer to a selected output cell buffer through an interconnection established in a switch fabric.
Since a limited amount of shared buffer memory is used to form a number of input/output cell buffers in a cell buffer module, it is necessary to allocate an appropriate buffer to each input/output port. If the amount of allocated memory is larger than necessary, the use efficiency of the shared buffer is decreased. Contrarily, if the amount of allocated memory is smaller than necessary, the required QoS (Quality of Service) such as Cell Loss Ratio cannot be satisfied.
Accordingly, buffer allocation needs to be adjusted by properly monitoring a cell buffer use rate. Moreover, by monitoring the cell buffer use rate, the traffic in an ATM switching system can also be analyzed and thereby the optimum network can be constructed by redistributing network equipment such as a buffer module.
As one example of a conventional ATM-related technique, there has been disclosed an ATM network system in Japanese Patent Application Unexamined Publication No. 10-322360. More specifically, the conventional ATM network system has a buffer use rate monitoring means and a transmission means. The buffer use rate monitoring means monitors the use rate of an input/output buffer in each node of the ATM network. When the monitoring means detects that the use rate exceeds a first threshold indicating the congestion state, the transmission means generates a cell indicating a congestion state and transmits it to anther node. When the monitoring means detects that the use rate is lower than a second threshold indicating the non-congestion state, the transmission means generates a cell indicating a non-congestion state and transmits it to another node.
The above-described conventional ATM network, however, does not disclose now to obtain a cell buffer use rate. Further, if a cell buffer use rate is obtained by totaling occupied amounts of all cell buffers used to store received cells, then a much large memory is necessary in proportion to the number of cells received and a monitoring time period.
An object of the present invention is to provide a cell buffer use rate monitoring method and system allowing a memory required for detecting the currently used amount of a cell buffer to be reduced.
According to the present invention, a method for monitoring a use rate of a cell buffer in an ATM (asynchronous transfer mode) switch, wherein the cell buffer is connected to a line in an ATM network, includes the steps of: a) setting a predetermined monitoring time period and a plurality of cell buffer thresholds: b) counting cells received at the cell buffer for the predetermined monitoring time period to produce a received cell count; c) detecting a currently used amount of the cell buffer; d) counting a number of times the currently used amount of the cell buffer has exceeded each of the plurality of cell buffer thresholds for the predetermined monitoring time period to produce a threshold-excess count; and e) calculating the use rate of the cell buffer based on the received cell count and the threshold-excess count.
The step (c) may include the steps of: c.1) incrementing a cell counter when a cell has been received at the cell buffer; c.2) decrementing the cell counter when a cell has been transmitted from the cell buffer; and c.3) detecting a current value of the cell counter as the currently used amount of the cell buffer.
The step (d) may include the steps of: d.1) when a cell has been received at the cell buffer, determining whether the currently used amount of the cell buffer exceeds each of the plurality of cell buffer thresholds; d.2) only when the currently used amount of the cell buffer exceeds each of the plurality of cell buffer thresholds, incrementing a threshold-excess counter; and d.3) detecting a value of the threshold-excess counter as threshold-excess count when the predetermined monitoring time period has elapsed.
In the step (e), the use rate RUSE of the cell buffer is calculated by RUSE=B/Sxc3x97100(%), wherein
for N greater than 1, B=SUM(|Hi+1xe2x88x92Hi|xc3x97Ci)+HNxc3x97CN, and
for N=1, B=H1xc3x97C1,
where B is a total buffer used amount of the cell buffer, S is the received cell count, Ci (i=1, 2, . . . N) is an ith cell buffer threshold of the plurality of cell buffer thresholds, Hi is the number of times the currently used amount of the cell buffer has exceeded the ith cell buffer threshold, and SUM(|Hi+1xe2x88x92Hi|xc3x97Ci) is defined as the sum total of (|Hi+1xe2x88x92Hi|xc3x97Ci) from i=1 to i=Nxe2x88x921.
In the step (a), a predetermined monitoring time period and a plurality of cell buffer thresholds may be allowed to be changed for each of the lines.
The ATM switch may include a plurality of cell buffers each corresponding to different QoS (quality of service) classes.
In the step (a), the plurality of cell buffer thresholds may correspond to different cell lose priorities.
According to another aspect of the present invention, an ATM switching system includes; a switch section having a plurality of cell buffers each connected to lines in an ATM network; and a cell buffer use rate monitor for monitoring a use rate of a cell buffer connected to a line The cell buffer use rate monitor comprises; a memory for setting a predetermined monitoring time period and a plurality of cell buffer thresholds, a cell detector for detecting reception and transmission of a cell; a counting controller for counting cells received at the cell buffer for the predetermined monitoring time period to produce a received cell count, counting a currently used amount of the cell buffer, and counting a number of times the currently used amount of the cell buffer has exceeded each of the plurality of cell buffer thresholds for the predetermined monitoring time period to produce a threshold-excess count; and a calculator for calculating the use rate of the cell buffer based on the received cell count and the threshold-excess count.